linux-kernel - Re: [PATCH 12/19] twl4030: mfd_cell is now implicitly available to drivers

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Date:	Wed, 2 Feb 2011 22:53:39 -0800
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	Andres Salomon <dilinger@...ued.net>
Cc:	Samuel Ortiz <sameo@...ux.intel.com>, linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Peter Ujfalusi <peter.ujfalusi@...ia.com>,
	Liam Girdwood <lrg@...mlogic.co.uk>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	Timur Tabi <timur@...escale.com>, linux-input@...r.kernel.org,
	alsa-devel@...a-project.org
Subject: Re: [PATCH 12/19] twl4030: mfd_cell is now implicitly available to
 drivers

On Wed, Feb 02, 2011 at 10:39:59PM -0800, Andres Salomon wrote:
> On Wed, 2 Feb 2011 22:05:21 -0800
> Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:
> 
> > On Wed, Feb 02, 2011 at 08:15:22PM -0800, Andres Salomon wrote:
> > >  static int __devinit twl4030_vibra_probe(struct platform_device
> > > *pdev) {
> > > -	struct twl4030_codec_vibra_data *pdata =
> > > pdev->dev.platform_data;
> > > +	struct twl4030_codec_vibra_data *pdata =
> > > platform_get_drvdata(pdev);
> > 
> > No, device's drvdata belongs to _this_ driver, and it is supposed to
> > manage it and use as it sees fit.
> 
> Right, so it's used to pass data to the probe function; once the probe
> function has obtained the pdata pointer, it's free to do with it what
> it will.
> 
> 
> > 
> > Note platform_set_drvdata(pdev, info) later in this function along
> > with platform_set_drvdata(pdev, NULL) in twl4030_vibra_remove(),
> > which means that with your change you will be able to bind the device
> > only once.
> > 
> 
> Hm, good point; if the driver is reloaded, the pdev that was created by
> mfd-core will have lost the pointer to pdata.
> 
> I wonder if I should be using mfd's driver_data instead. I used
> platform_data because a bunch of drivers had already made use of it to
> pass cell information..

Then they are doing it incorrectly. One possible way is to have parent
device carry relevant data in its drvdata and have children get it from
there.

-- 
Dmitry
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